1. Field of the Invention
This invention relates to a shift range device for an automatic transmission used in an automotive vehicle and more particularly to a shift range device for an automatic transmission used in an automotive vehicle such as a truck or a bus and which is not provided with a park position of the shift range.
2. Description of the Related Art
An automatic transmission for relatively a small size automotive vehicle, such as a private car, is generally provided with a parking position "P" at an upper end of a shift position of a shift range selector device. A parking mechanism which is operable corresponding to the operation of a shift lever, as shown in FIG. 3, is disclosed in Japanese Laid Open Patent No. 59-184049 published without examination in 1984. When the shift lever (not shown) is shifted to the park position "P", the shift lever is connected to a lever 1 and a rod 2 by a link mechanism (not shown). The lever 1 and the rod 2 are moved in the leftward direction in FIG. 3 in response to the operation of the shift lever (not shown). Thereby, a pawl 4 having an engaging portion is moved in the upper direction by a cam 3 which is formed at one end of the rod 2. Accordingly, the engaging portion of the pawl 4 is engaged with a parking gear (not shown). As a result, the shift change into the park position "P" is completed.
However, an automotive vehicle of large size like a truck and a bus cannot be provided with the foregoing parking mechanism because of insufficient mechanical strength of the engaging portion with the cam 3. Thus, as shown in FIG. 4, a shift range device which is disclosed in "MOTOR VEHICLE" VOL. 39, September 1989 is not provided with the park position "P", and also an example of the shift range device which is not provided with the park position "P" is disclosed in "HT700D Series Service Manual" published in March, 1976 by Allison Diesel Company.
However, the foregoing conventional shift range device has the following problem. Namely, when the shift selector lever 5 is shifted to the upper end position in FIG. 4, the shift position is shifted to a reverse position "R". Therefore, there is a fear that the car would suddenly move in the backward direction if the driver does not depress a brake pedal (not shown).